This invention relates to an ion exchange process.
The plug flow process for operating ion exchange runs by having ion exchange resin (IOR) filled into suitably designed columns with the feed solution being fed vertically upward or downward, as desired, entering first one column and then on to the next absorbing the TDS (total dissolved solids) and exchanging the target cations for H+ and the target anions for OH−. The final water will emerge being essentially free of TDS and neutral—the exchanged H+ and OH− having neutralised each other to produce further water. When the first catex column has become exhausted this one will be taken out of service—by changing a suite of valves—and be rinsed free of the feed water and then be regenerated by an acid to reverse the exchange procedure, exchanging the extracted target cations for H+ back onto the resin. Any residual acid will have to be rinsed off the resin before this regenerated column is returned back to service in the extraction train of columns. The exact but opposite routine is operated for the anex columns but that alkali is used to replenish the OH− sites on the anex resins. This process is repeated on a never ending routine so that fresh resin is always presented to the incoming feed water and the columns are taken out of service on a carousel-like fashion after rinsing to be regenerated as needed.
The entire above configuration is expensive and extremely cumbersome to design, build and to operate and requires large amounts of good quality rinse water in between each operation to prepare the various columns for service.
Ion exchange processes can also be carried out in a continuously stirred tank reactor (CSTR). In such a process the ion exchange resin is contained in its own tank by a screen at the top of the tank that allows the water phase to overflow into a collection gutter while the OR circulates inside the tank to give good mixing of the resin with the water phase to achieve the exchange needed. The IOR can be kept in suspension by designing the CSTR's in a conical fashion so that the vertical flow rate is greatest at the bottom of the tank and slowest at the top. It is also desirable to stir the contents by using an external pump which only contacts the water phase thus ensuring that the IOR never gets sheared by a fast moving pump impeller. Alternatively the CSTR can be stirred by a specially selected gentle aerofoil stirrer to keep the IOR uniformly dispersed in the reactor.